The invention relates to a slot-closing device for closing a slot in a stator or rotor of an electric machine. The slot-closing device enables electrical conductive elements, for example copper bars, by means of which a three-phase winding is formed, to be fixed or retained in position in the slot. Also included in the invention are a device which can be embodied as a stator or rotor and a method for closing a slot of the stator or rotor.
The slots of electric machines serve to accommodate the insulated electrical conductive elements or, as the case may be, an arrangement of such conductive elements. The slots generally have a slot opening which is directed toward the air gap of the electric machine. The conductive elements can be inserted into the slot by way of the slot opening during the manufacture of the electric machine. In particular in the case of high-voltage machines, the practice is to make use of what are termed open slots, in which the slot opening extends over the entire slot width.
Once the conductive elements have been inserted, the slot opening must be closed in order to prevent the conductive elements from working their way up and out of the slot during the operation of the electric machine. The slot closure is usually achieved by means of solid slot closure elements, known as slot wedges. Said slot wedges may be fabricated for example from technical laminated materials by mechanical processing. Equally, they may be fabricated from thermoplastic or duroplastic molding materials by means of strand extrusion or injection molding.
The slot closure materials can be non-magnetizable composites, which therefore make no effective contribution to the magnetizability of the stator, as a result of which the power factor, efficiency and heat buildup, and consequently resistive losses, can exhibit unfavorable values.
In order to improve the magnetic flux guidance in the region of the slot opening, slot closures can be embodied in part using soft-magnetic materials, for example by means of iron-filled ferritic laminated materials. Such a slot-closing device is known from EP 2 706 649 A1, for example.
A major disadvantage with soft-magnetic slot-closing devices is that on account of the hard material used it is not possible to guarantee the permanent tightness of fit in the slot, because the soft-magnetic material executes a proper motion due to the magnetic alternating loads during the operation of the machine in combination with thermal load, thermomechanical alternating load and environmental influences, as a result of which proper motion the slot-closing device can shake itself loose.
It is known from EP 2 706 649 A1 to mechanically deform a slot wedge in order by this means to spread or expand it in a slot. At the same time an electrically insulating layer can also be sandwiched between the slot wedge and a slot wall. In this case a laborious and time-consuming operation is required in order to fix the insulating layer in place during the expansion of the slot wedge.